Mineral Textures Research Articles

TEXTURAS DOS MINERAIS DE MINÉRIO DA REGIÃO AMAZÔNICA. PARTE 1

Ore minerals are usually characterized to the formation of mineral deposits. Textures can provide evidence of the nature of processes such as initial ore deposition, post-deposition rebalancing or metamorphism, deformation, annealing and weathering. The recognition and interpretation of textures is usually the most important step in understanding the origin and evolution of an ore. As they are ores that contain high economic value, and their study is necessary to correctly define the metallurgical alternatives for an adequate process of obtaining metallic products. Among the most important mines that are operating in Carajás are N4 (iron), Azul (manganese), Sossego and Salobo (copper) and Onca Puma (nickel). Most ores, show opaque characteristics that can be well studied by microscopy of opaque minerals, but others with SEM/EDS. The textures of these ore minerals are distinctive among them, highlighting the disseminated copper minerals subject to mineral liberation and micritic manganese minerals and fines granulates nickel-bearing minerals, ready for metallurgical extraction. Keywords: bornite; chalcopyrite; cryptomelane; chysotile; lizardite.

The Geochemical and Textural Transition between the Reef Package and its Hanging Wall, Stillwater Complex, Montana, USA

Abstract The highest grade Pd-Pt deposit on Earth, the J-M Reef, is hosted in coarse-grained to pegmatoidal cumulates called the Reef Package. Decades of mine development of the J-M Reef have revealed that a distinct discontinuity in rock fabric marks the top of the rock unit that hosts economic-grade sulfide mineralization. Mine geologists refer to this discontinuity as the hanging wall contact. This contact is the top of the Reef Package and is always locatable—either by the change in rock fabric or by distinctive hanging wall textures of silicate minerals—even when the reef sulfide mineralization is absent. This rather subtle textural feature is used reliably by mine geologists to follow the Reef during exploration and mine development. Although some high tenor sulfides (>1000 ppm Pd in 100% sulfide) are found sporadically in the hanging wall cumulates, these accumulations are too small to be economically viable. We present quantitative rock fabric data for four Reef Package and hanging wall intersections collected by electron back-scattered diffraction (EBSD). Plagioclase fabrics in the hanging wall are characterized by low variance in grain sizes and a strong point maximum concentration of (010) and a perpendicular girdle distribution of [100] consistent with an axial B-type fabric. These fabrics are indicative of either compaction of the crystal mush or crystal settling of nucleated crystals, the bulk magma in a chamber. Conversely, the fabrics of the Reef Package show higher variance grain in size distributions and weak to undeveloped preferred orientation of plagioclase crystals that did not undergo significant alignment or textural equilibration of plagioclase grains. The absence of foliation in the Reef Package stands in contrast both to hanging wall fabrics and to other reported EBSD datasets of plagioclase crystals orientations from the Bushveld Complex, the Skaergaard Intrusion, and the Rum Intrusion. Furthermore, plagioclase crystal size distributions for the Reef Package show flatter slopes and convex profiles with fewer crystals at small size fractions indicating the dissolution of small crystals during partial melting and textural coarsening (i.e. Ostwald ripening) and crystal growth. Crystal growth was favored over the nucleation of new crystals during prolonged interaction with a hot infiltrating melt into the resident mush resulting in the coarse-grained textures of the Reef Package cumulates. The hanging wall contact represents a boundary between partially remelted crystal mush of the Reef Package, where sulfide mineralization formed and accumulated, and an overlying essentially barren cumulate pile. The hanging wall cumulates formed following the cessation of footwall erosion and the resumption of crystal accumulation by normal magma chamber processes.

Quantitative phase analysis and rietveld texture determination of minerals in ash deposits in a 11.2 MW moving grate boiler

Some ash deposits were sampled from a 11.2 MW moving grate boiler to study the mineral transformation, ash deposition and mineral texture evolution behavior, which were determined by different analytical methods. Rietveld refinement was applied to determine the mineralogy, refine the crystallographic structures of minerals, and characterize texture heterogeneity of minerals in ash deposits. The results presented that the major mineral phases in ash deposits were identified as silicates, oxides, sulphates, sulfides and carbonates. The phase transformation between minerals during combustion was proposed. The variation of the diffraction peak intensities indicated the existence of the weak and strong textures. The texture indexes were larger than one mrd2 for most minerals, implying strong preferred orientation distributions, while the texture indexes of some other minerals were approaching one mrd2, indicating the existence of weak and random textures. Some pole figures showed strong texture features with a high degree of texture disorder in these minerals, while other minerals displayed weak textures with low volume diffractions of preferred orientations in these mineral phases. Owing to the diffraction peak overlapping of different minerals, different texture components with fibre-like or biaxial-like characteristics were found in ash deposits.

Multi-stage construction of the Little Cotton wood stock, Utah, USA: Origin, intrusion, venting, mineralization, and mass movement

AbstractMany porphyry molybdenum deposits are hosted in multi-phase plutons, but it is unclear in some deposits how these magmas originated and whether the pluton intruded as it fractionated or was intruded by new batches of magma. New mapping has clarified field relationships between units in the White Pine porphyry Mo system hosted in the Little Cottonwood stock, Utah (western United States), including the White Pine intrusion, the Red Pine porphyry, rhyolite dikes, and phreatomagmatic pebble dikes. Geologic relations and geochemistry show the system formed in a continental arc setting during rollback of the subducting Farallon slab rather than during extension related to orogenic collapse. Whole-rock geochemistry shows distinct fractionation trends for each of the major intrusive units in the composite pluton, suggesting they formed separately, which is supported by new U-Pb zircon laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) ages of ca. 30 Ma for the Little Cottonwood stock, 27 Ma for the White Pine intrusion, and 26 Ma for the previously undated Red Pine porphyry. Mineral textures, cross-cutting relationships, and alteration mineralogy indicate that intrusion of the youngest phase led to a fluid-saturated magmatic system and triggered venting, including emplacement of pebble dikes. In the adjacent east Traverse Mountains, pebble dikes contain clasts that have similar mineral assemblages, textures, and ages as the major igneous units in the White Pine deposit. This indicates that the pebble dikes in east Traverse Mountains and in the pluton are the upper and lower parts of the same magmatic-hydrothermal system, which was decapitated by a mega-landslide that was likely facilitated by alteration in the Oligocene hydrothermal system and by later Basin and Range faulting.

Magnetite geochemistry and iron isotope signature of disseminated and massive mineralization in the Kalatongke magmatic Cu[sbnd]Ni sulfide deposit, northwest China

Magnetite is a common accessory mineral and an indicator to magma evolution and sulfide fractional crystallization in magmatic NiCu sulfide deposits. The Kalatongke magmatic sulfide deposit at the southern margin of the Central Asian Orogenic Belt is composed of 11 mafic intrusions. The sulfide orebodies (Y1, Y1 deep, and Y2) are hosted by three small mafic intrusions, and magnetite is common in all mineralized samples. Based on ilmenite exsolution texture, composition, and type of mineralization, three types of magnetite are identified, (1) primary Fe-rich magma-related magnetite (type 1), (2) sulfide liquid-related magnetite (type 2), and (3) hydrothermal magnetite (type 3). We speculate that Fe isotope equilibrium fractionation between early or co-crystallized light 54Fe-enriched sulfide and magnetite may account for the ultra-high magnetite δ56Fe value (0.70‰ to 1.35 ‰) in the magmatic magnetite (types 1 and 2). Enriched compatible elements in type 1 magnetite (TiO2 = 1.52 wt% to 7.89 wt%, V = 775 ppm to 2420 ppm, Cr = 2697 ppm to 14,658 ppm, and Ni contents = 478 ppm to 1256 ppm), reflect the characteristics of primary Fe-rich magmatic magnetite crystallized at relatively high temperature and low oxygen fugacity. Type 2 magnetite in massive ores has Ni (762 ppm to 1769 ppm) and δ56Fe (0.89 ‰ to 1.10 ‰) values similar to type 1 magnetite, but significantly lower TiO2, V and Cr contents (TiO2 = 0.07 to 3.72 wt%, V = 61 to 2314 ppm, Cr = 5 to 2937 ppm), indicating co-crystallization with an evolved sulfide liquid across a wide span of temperature and oxygen fugacity. Type 3 magnetite is of hydrothermal fluid origin, with low δ56Fe (0.29 ‰ to 0.41 ‰) and Ni (177 ppm to 377 ppm).Magnetite composition and Fe isotope signatures at the Kalatongke magmatic sulfide deposit can reveal the genesis of magnetite and the evolution of the melt and sulfide. The Y1 orebody was completely crystallized over a short period of time, while the Y1 deep and Y2 east orebodies underwent a protracted evolution during which magnetite co-crystallized from primitive Fe-rich melt, Fe-rich evolved melt and Cu-rich intermediate sulfide solution. Magnetite and sulfide in the Y2 west massive orebody likely formed last. The compatibility of both lithophile and chalcophile elements, combined with Fe isotopes in magnetite, makes magnetite a good indicator of silicate and sulfide melt evolution.

Magma mixing for the genesis of Neoproterozoic Mopanshan granitoids in the western Yangtze Block, South China

Crust- and/or mantle-derived igneous rocks in the Neoproterozoic continental magmatic arc along the western Yangtze Block (South China) have been extensively studied, but the crust-mantle interaction that might have been involved in the formation of these rocks was poorly understood. In this paper, we present an integrated study on petrology, whole-rock compositions, in-situ plagioclase Sr and zircon U-Pb-Hf isotopes for granodiorites and monzogranites from the Neoproterozoic Mopanshan pluton in the western Yangtze Block. Our objective is to provide vital constraint on the magma mixing process in the formation of these rocks. The new LA-ICP-MS zircon U-Pb dating results reveal that both granodiorites and monzogranites of the Mopanshan pluton were coeval and formed at ca. 820 Ma. They are calc-alkaline to high-K calc-alkaline (SiO2 = 66.06–70.30 wt%, K2O = 2.24–3.34 wt%) and metaluminous to slightly peraluminous (A/CNK = 0.99–1.10) rocks, and characterized by middle-upper crustal trace element patterns (e.g., enrichment in Rb, K, Th, U, and Pb, and depletion in Nb, Ta, Sr, and Ti). The magma mixing process is supported by following ample evidence, including (1) the disequilibrium mineral textures and an abruptly increased An values (up to 60) as well as significant decrease of (87Sr/86Sr)i ratios from core to rim in plagioclase crystals, (2) higher Mg# values (45–50 > 40) than those of experimental melts from basalts at the same silica contents, (3) positive and negative whole-rock εNd(t) (–0.72 to + 1.01) values as well as variable whole-rock (87Sr/86Sr)i (0.702778–0.705404) and zircon εHf(t) (+1.76 to + 7.72) values. The special geochemical characteristics and element modeling support that the Mopanshan pluton was generated by magma mixing of ancient crust-derived melts and relatively mafic melts from metasomatized mantle source. The adakitic signatures observed in the Mopanshan pluton were attributed to subsequent hornblende-dominant intra-crustal fractional crystallization, rather than derived from a thickened lower crust source. In combination with regional geology and our compilation for Nd-Hf isotopes of Neoproterozoic igneous rocks, the Mopanshan pluton is magmatic response of intensive crust-mantle interaction induced by underplating of voluminous mantle-derived magma in a back-arc extension setting. This research highlights that the crust-mantle interaction is significant for the petrological and geochemical diversity of Neoproterozoic granitoids from the western Yangtze Block.

Automated Segmentation of Olivine Phenocrysts in a Volcanic Rock Thin Section Using a Fully Convolutional Neural Network

An example of automated characterization and interpretation of the textural and compositional characteristics of solids phases in thin sections using machine learning (ML) is presented. In our study, we focus on the characterization of olivine in volcanic rocks, which is a phase that is often chemically zoned with variable Mg/(Mg + Fe) ratios, so-called magnesian number or mg#. As the olivine crystals represent only less than 10 vol% of the volcanic rock, a pre-processing step is necessary to automatically detect the phases of interest in the images on a pixel level, which is achieved using Deep Learning. A major contribution of the presented approach is to use backscattered electron (BSE) images to: 1) automatically segment all olivine crystals present in the thin section; 2) determine quantitatively their mg#; and 3) identify different populations depending on zoning type (e.g., normal vs reversal zoning) and textural characteristics (e.g., microlites vs phenocrysts). The segmentation of the olivine crystals is implemented with a pretrained fully convolutional neural network model with DeepLabV3 architecture. The model is trained to identify olivine crystals in backscattered electron images using automatically generated training data. The training data are generated automatically from images which can easily be created from X-Ray element maps. Once the olivines are identified in the BSE images, the relationship between BSE intensity value and mg# is determined using a simple regression based on a set of microprobe measurements. This learned functional relationship can then be applied to all olivine pixels of the thin section. If the highest possible map resolution (1 micron per 1 pixel) is selected for the data acquisition, the full processing time of an entire thin section of ∼3×4cm containing more than 1,500 phenocrysts and 20.000 microliths required 140 h of data acquisition (BSE + X-Ray element maps), 8 h of training and 16 h of segmentation and classification. Our further tests demonstrated that the 140 h of data acquisition can be reduced at least by a factor of 4 since only a part of the thin section area (25% or even less) needs to be used for training. The characterization of each additional thin section would only require the BSE data acquisition time (less than 48 h for a whole thin section), without an additional training step. The paper describes the training and processing in detail, shows analytical results and outlines the potential of this Deep Learning approach for petrological applications, resulting in the automatic characterization and interpretation of mineral textures and compositions with an unprecedented high resolution.

A high-efficiency gold precipitation model associated with Fe carbonates: Example from the Jiudian deposit of the world-class Jiaodong gold province

Pyrite (FeS2) is a common host for gold in various hydrothermal gold deposits, but the close relationship between siderite (FeCO3) and gold is rarely reported. Furthermore, the gold precipitation mechanism is also poorly understood. In the Jiudian gold deposit of the world-class Jiaodong gold province (eastern China), two gold ore stages were identified: pyrite-smoky grey quartz (the first ore stage), quartz-siderite-polymetallic sulfide (the second ore stage). Gold occurs as visible electrum with minor native gold in both ore stages. The latter stage ores have higher gold grade, indicating gold precipitation associated with second-stage siderite is more efficient than that associated with first-stage pyrite. An integration of mineral texture and composition and fluid inclusion evidence demonstrates that gold deposition in the first ore stage was formed by fluid immiscibility, which destabilized the Au (HS)2− complex in the ore-forming fluid. Fluid immiscibility (boiling) also occurred in the second ore stage, resulted from the abrupt drop of pressure and temperature due to the fracturing of the ore-controlling faults during seismic activity and mixing with cold oxidized meteoric water, and then the polymetallic sulfide precipitation was triggered. The presence of CH4 in the hydrothermal fluid of the second ore stage may have also promoted the fluid unmixing. Subsequently, the metasomatic reactions of pre-existing pyrite into marcasite and siderite occurred successively, and further facilitated with fluid immiscibility mutually by building a positive chain circuit. These complex processes may have formed a highly drastic and disequilibrated fluid system, in which the crystallized pyrite is featured by the decoupling of As and Au, which is different from the common early-ore Au-As association. The abnormal hydrothermal physicochemical perturbance may have triggered high-efficient gold precipitation associated with siderite.

Zircon as a Recorder of Trace Element Changes during High-Grade Metamorphism of Neoarchean Lower Crust, Shevaroy Block, Eastern Dharwar Craton, India

AbstractSystematic changes in whole-rock chemistry, mineralogy, mineral textures, and mineral chemistry are seen along a ca. 95-km traverse of late Archean granitoid orthogneisses in the Shevaroy Block, Eastern Dharwar Craton, southern India. The traverse passes from amphibolite-grade gneisses in the north to granulite-grade rocks (charnockite) in the south. Changes include whole-rock depletion of Rb, Cs, Th, and U in the granulite grade rocks as relative to the amphibolite grade gneisses, and oxidation trends regionally from highly oxidised granulite-facies rocks near the magnetite–haematite buffer to relatively reduced amphibolite-facies rocks below the fayalite-magnetite-quartz. Rare earth elements show limited mobility and are hosted a variety of minerals whose presence is dependent on the metamorphic grade ranging from titanite and allanite in the amphibolite-facies rocks to monazite in the vicinity of the orthopyroxene-in isograd to apatite in the granulite-grade charnockite. Cathodoluminescence and back-scattered electron sub-grain imaging and sensitive high-resolution ion microprobe analysis of zircon from 29 samples of dioritic, tonalitic, and granitic orthogneiss from the traverse reveals magmatic zircon cores that record the emplacement of the granitoid protoliths mostly about 2580 to 2550 Ma, along with a few older mid to late Archean tonalites. Protolith zircon was modified during metamorphism by overgrowth and/or replacement. Relative to igneous cores, U-enriched metamorphic zircon, dominant in the amphibolite-grade gneisses, formed at ca. 2530 Ma, predating retrograde titanite growth at ca. 2500 Ma. Uranium-depleted mantles grew on zircon between 2530 and 2500 Ma in granulite-grade samples south of the orthopyroxene-in isograd. In some of these samples, the U-depleted metamorphic zircon is preceded by mantles of U-undepleted zircon, indicating a progression of metamorphic zircon growth with increasingly depleted compositions between 2530 and 2500 Ma. With increasing metamorphic grade (from amphibolite to granulite) and oxidation state, allanite and monazite disappear from the assemblage and zircon became depleted in U and Th. Whole-rock U-Th compositions became decoupled from relict magmatic zircon compositions, reflecting the development of U-depleted metamorphic zircon and indicating that whole-rock chemical differences along the traverse were produced during metamorphism, rather than just reflecting differences in dioritic vs granitic protoliths. Although in situ anatexis and melt extraction may have played a role, whole-rock and zircon depletion of trace elements can be explained by the action of externally derived, oxidising, low-H2O activity hypersaline fluids migrating up through the mid to lower crust. Fluids and element migration during metamorphism may be the end result of subduction related processes that cumulated in the collision and concatenation of island arcs and continental blocks. These tectonic processes assembled the Dharwar Craton at the end of the Archean.

Unsupervised textural classification of rocks in large imagery datasets

• Rock imaging characterisation techniques capture composition and texture. • A new feature extraction method for rock texture from imaging data is documented. • A large dataset of hyperspectral rock images was classified using this new method. • The results prove a robust and repeatable approach for textural analysis. • Textural outputs can be incorporated in geometallurgical modelling. The value of rock characterisation, whether it is for mineral exploration , extraction, or concentration, lies in the ability to describe its composition and texture. In the past century, extensive technological developments have provided new opportunities to assess compositional properties, both geochemical and mineralogical, and at different scales: X-ray diffraction, X-ray fluorescence, inductively coupled plasma mass spectrometry , reflectance spectroscopy , etc. More recently, the advent of imaging characterisation techniques and high-performance computing power has enabled the assessment of mineral texture in a robust and quantitative manner. This study proposes and validates an end-user focused workflow for the identification of textural families in a large drill-core hyperspectral imagery dataset, based on a novel textural feature extraction method named Mineral Co-Occurrence Probability Field (MCOPF). This workflow combines vintage image textural assessment methods with modern machine learning techniques for the automated unsupervised classification of textures within a drill core hyperspectral imagery dataset. The results demonstrate a meaningful and robust identification of rock textural families (clusters), enabling a wide range of applications in geology, mining, and metallurgy in the academic and industrial sectors.

Growth and evolution of long-lived, large volcanic clusters in the Central Andes: The Chachani Volcano Cluster, southern Peru

In the Central Andes, large (> 500 km2) and long-lived (1–5 Ma) volcanic clusters (LVCs) are less explored and their eruptive history and magmatic regimes less understood than smaller, short-lived (<0.5 Ma), individual stratocones. The Chachani-large volcanic cluster (C-LVC) sizeable volume (c. 290 km3) consists of twelve edifices forming the 1.06–0.64 Ma group of stratovolcanoes and the 0.46–0.05 Ma group of domes coulees and block-lava flow fields. Both groups overlie pre-Chachani lavas and tuffs 1.02–1.27 Ma, and together they have buried large nested craters or a caldera associated with the c. 1.62–1.66 Ma Arequipa Airport ignimbrite. The C-LVC evolved from: (i) homogeneous compositions of the pre-Chachani and Chachani basal eruptive units to (ii) relatively wide compositional variations (53–67 wt% SiO2) between mafic andesite and dacite at moderate eruptive rates (0.27–0.41 km3/ka) for the ‘Old Edifice’ group, and finally to (iii) narrower (57–64 wt% SiO2) andesitic compositions coinciding with extrusive activity at 2.5 times lower eruptive rates (0.12–0.15 km3/ka) for the ‘Young Edifice’ group. The large compositional variations in the Old Edifice group are related to strongly contrasting resident and recharge magma compositions of hybridized lavas. In contrast, the narrow compositional range and lower eruption rate during the second half of the C-LVC eruptive history represent a trend towards more homogeneous, andesitic magma composition with time. Mineral texture and compositional studies provide evidence for disequilibrium and magma mixing in the C-LVC shallow (5–20 km depth range) magma reservoirs. These temporal changes in magma composition document that the transcrustal magma systems of the C-LVC evolved and matured with time by a combination of processes: fractional crystallization, crustal contamination and magma mixing/mingling with variable rates of mafic recharge. This resulted in a shift in time to a steady state, monotonous (andesite) regime as a result of coupling between compositional parameters and thermal conditions, density constraints, and the viscosity/crystallinity of erupted magmas.

Rock Physics Model Provides Insight Into Reservoir Characterization

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30359, “Reservoir Characterization Supported by Rock Physics Diagnostics,” by Stephan Gelinsky, Shell. The paper has not been peer reviewed. Copyright 2021 Offshore Technology Conference. Reproduced by permission. Rock physics models are often perceived as too complicated and dependent on too many difficult-to-measure parameters to be of practical use for reservoir characterization. In the complete paper, the author demonstrates how careful calibration of a common and simple rock physics model can provide valuable insights into the reservoir and seal elastic properties such as function of porosity, fluid, and mineral properties and net-to-gross. The model can be used for quantitative seismic interpretation of reservoirs with variable net-to-gross and porosity away from well control. Methodology Rock physics describes the application of fundamental physical principles to establish the elastic properties of porous rocks as a function of their mineral composition, pore fill, and microstructure and texture. Once a suitable rock physics model is calibrated locally, the use of seismic data to estimate reservoir rock and fluid properties from the elastic rock properties is possible—specifically, from the observed seismic amplitudes and if seismic data were inverted from the seismically derived acoustic and shear impedances. The Hashin-Shtrikman (HS) effective medium bounds can be used to characterize both sandstones and shales. While the application of this model for clean sandstones is straightforward and, thus, is not included in this synopsis, the application for shales is more complex.

Deformation mechanisms and characteristics of the meta-BIFs from an early Proterozoic shear system of the Southern Granulite Terrane (SGT), India

We studied three samples of Banded Iron Formation (BIF) rocks from Southern Granulite Terrane (SGT) of India, which was metamorphosed at high-pressure granulite facies and exhumed from 40 to 50 km depth. We examined the microstructure, texture, and deformation mechanisms of the primary minerals (quartz, magnetite, and hematite). Microstructures, variations in size and shape of quartz grains suggest that the three samples deformed to different intensities and temperatures. The EBSD derived CPOs for quartz and magnetite grains are strong, implying dislocation creep as the dominant mechanism. The presence of distinct subgrains in magnetite, rare in natural samples, attests to the same. Furthermore, twinning on {111}, as evident from the misorientation angle and axis distributions, indicates ductile deformation of magnetite below 400 °C. Subgrain boundary trace analysis in selected magnetite grains reveals that multiple-slip planes {111}, {110}, and {100} were operational. Topotaxial replacement, via redox reaction, of magnetite grains along their octahedral planes by hematite is evident. Well-developed CPOs but low (<1°) GOS values of both magnetite and hematite grains suggest that recovery processes in these were rapid. Post-replacement deformation was weak and did not affect the hematite CPOs that were inherited from the relatively more deformed host magnetite grains.

Zeolite Minerals from Wat Ocheng, Ta Ang, Ratanakiri Province, Cambodia – Occurrence, Composition, and Paragenesis

ABSTRACT Located in the southwest corner of the Ratanakiri Volcanic Province, the Wat Ocheng basalt is the first known zeolite locality in Cambodia. The basalt is a fine-grained, vesicular to amygdaloidal, subalkaline to transitional alkaline intraplate tholeiite comprised of 30% lath-like plagioclase (average: Ab51An45Or4), 35% interstitial augite (average: Wo44En35Fs21), 25–30% zeolites after plagioclase and volcanic glass, and minor skeletal ulvöspinel. It contains mineralized amygdales ranging in size from 0.5 × 0.5 cm to 5 × 9 cm. Nine zeolite species occur at Wat Ocheng, including analcime, chabazite-Ca, gonnardite, natrolite, phillipsite-Ca, and thomsonite-Ca, along with clays, aragonite, calcite, and pyrite. All the zeolite species are being described from Cambodia for the first time. The zeolite and secondary mineral assemblages observed at Wat Ocheng are similar to those reported from other alkaline basalt localities, including those in neighboring Vietnam, and are a product of alteration of the primary Ca-Na minerals and volcanic glass as a result of burial metamorphism and infiltration of heated meteoric waters. The mineral assemblage is not homogeneous across amygdales within the exposed lava flow, suggesting localized closed systems, likely the result of early precipitation of clay minerals and fine-grained zeolites. Decreased porosity and differences in fluid geochemistry would account for the diversity in the observed assemblages. Four stages of hydrothermal alteration and zeolitization have been defined based on mineral textures and chemistry. Zeolite formation began with fine-grained Ca- (chabazite-Ca and phillipsite-Ca) and Na- (analcime) dominant, high TSi (Si/Si+Al) species in Stage II following deposition of clay minerals in Stage I. Stage III is characterized by increasing Na+K contents and decreasing TSi. Crystallization of coarse-grained chabazite-Ca and phillipsite-Ca with increasing Na+K contents in the rims of the crystals followed the development of natrolite with a later-stage epitaxial overgrowth of thomsonite-Ca. The final stage of mineralization (Stage IV) included late-stage calcite, pyrite, and termination of growth of acicular sprays of thomsonite-Ca. Post-magmatic cooling and circulation of meteoric water and fluids derived from alluvial sediments overlying the basalts were involved in zeolitization. Thermal sources include an underlying basaltic andesite flow as well as regional deep-seated, extensional pull-apart structures, the result of a thinned lithosphere and injection of fertile mantle following the collision of the Eurasian and Indochina plates during the Himalayan Orogeny.

Identification of Potential Glucosyltransferase Inhibitors from Cinnamic Acid Derivatives Using Molecular Docking Analysis: A Bioinformatics Study

Background: Dental caries is one of the most common oral chronic diseases. Streptococcus mutans is the main pathogenic bacteria playing a role in degrading the mineral texture of the teeth. Glucosyltransferase (GTFase) of S. mutans is responsible for producing glucan, which is the main exopolysaccharide found in the cariogenic biofilms. Further, previous studies have reported that cinnamic acid diminished biofilm formation of S. mutans. Therefore, we hypothesized that cinnamic acid and its derivatives might act as GTFase inhibitors. Methods: The binding affinity of a total of 12 plant-based compounds including cinnamic acid and its 11 derivatives to the GTFase active site were examined by utilizing the AutoDock tool. The possible interactions between top-ranked cinnamic acid derivatives and the residues within the GTFase catalytic site were also taken into consideration. Results: Five of the cinnamic acid derivatives including rosmarinic acid (RA), cynarine, chlorogenic acid (CGA), caffeic acid 3-glucoside, and N-p-coumaroyltyramine demonstrated inhibitory effects on GTFase at nanomolar concentration. Stabilizing interactions such as π–π stack pairing and pi-charge interactions were detected between top-ranked GTFase inhibitors and residues within the enzyme active site. Conclusions: The present study suggests that RA, cynarine, CGA, caffeic acid 3-glucoside, and N-p-coumaroyltyramine might have protective effects on dental caries, and therefore, may be considered as anti-tooth caries compounds.

Rock textures and mineral zoning – A clue to understanding rare-metal granite evolution: Argemela stock, Central-Eastern Portugal

The small leucocratic strongly peraluminous P, F, Li-rich granitic system at Argemela, central-eastern Portugal, is an ideal object for the study of relations between chemical composition of granitic rocks, rock-forming minerals and rock and mineral textures, and the associated Sn, Ta and W mineralization. To define the rock and mineral composition and to formulate an evolutionary model, traditional methods of bulk-rock chemical analyses, and EMPA and LA ICP-MS analyses of rock-forming minerals were combined with the study of macrotextures, TIMA-automated mineralogical mapping of typical rock samples, and CL study of internal texture of quartz and mica crystals. The Argemela stock forms a steep cylindrical body 1 km deep, with an elliptical outcrop 250 × 180 m in size, crosscutting Cambrian schists. The stock comprises two intrusions: a geochemically moderately evolved equigranular facies (0.3 wt% F, 1.2 wt% P2O5, 1850 ppm Li, 310 ppm Sn, 24 ppm Ta, 5 ppm W) composed of albite, quartz, muscovite and minor montebrasite followed by a rather inhomogeneous, more evolved porphyritic facies (0.25–1.2 wt% F, 1.3–1.8 wt% P2O5, 1600–4900 ppm Li, 600–1000 ppm Sn, 40–85 ppm Ta, 3–6 ppm W) composed of quartz, mica and subordinate K-feldspar phenocrysts embedded in an albite-quartz-mica-amblygonite matrix. The later facies is rimmed by stockscheider at the contact with slates, and with an up to 1 m thick layered zone with unidirectional solidification textures along contact with the equigranullar facies. The NE-part of the stock is crosscut by numerous thin quartz veinlets ±K-feldspar, phosphates and wolframite, while several aplitic dikes and thicker quartz+phosphate veins were found in two boreholes NW of the granite. Porphyritic facies, the most voluminous part of the system, contains strongly zoned phenocrysts of mica (phengite→lepidolite) and quartz (Ti-enriched to Al, Rb-enriched) indicating crystallization in two magmatic stages, while the equigranular facies and extragranitic aplitic dikes crystallized in one magmatic stage only. Hydrothermal muscovite enriched in Sn and Ta forms late overgrowths on some mica flakes in the porphyritic facies and in aplitic dikes. Based on a combination of chemical and textural observations, a four-stage evolutionary model of the Argemela stock was formulated: (i) an early magmatic stage comprises intrusion and in situ crystallization of aplitic dikes and the equigranular facies, and crystallization of quartz and mica cores in the deeper reservoir prior to intrusion of the porphyritic facies; (ii) in the late magmatic stage, crystal mush + evolved residual melt from the reservoir intruded upwards crystallizing the porphyritic facies including the stockscheider and layered zone. A small part of evolved melt formed rounded enclaves crystallizing as a phenocrysts-free ball facies. (iii) In the early (high-temperature) hydrothermal stage, magmatic fluid caused weak pervasive muscovitization of the porphyritic facies and aplitic dikes accompanied by the crystallization of disseminated cassiterite and columbite. After the transition from ductile to brittle deformation, quartz veinlets also developed, mainly in the NE part of the body. (iv) In the late, low-temperature stage, schist-derived fluid enriched in Ca, Sr and Ba caused local alteration of granite, forming crandallite–goyazite–gorceixite solid solution.

A bone to pick: stable isotope compositions as tracers of food sources and paleoecology for notosuchians in the Brazilian Upper Cretaceous Bauru Group

Notosuchia is a highly diverse group of crocodyliforms that peaked during the Cretaceous period. Their taxonomic abundance and morphological disparity in the Upper Cretaceous Bauru Group (Bauru Basin, Brazil) is remarkable, with over 20 species reported. The stable carbon and oxygen isotope composition of notosuchian bioapatite from two sites (i.e., the Ponto 1 do Price and Fazenda Três Antas) in west Minas Gerais State was analyzed to evaluate differences in feeding habits among the taxa found in both localities. Possible environmental stressors are examined, in parallel to sedimentological, paleopedological, and paleontological studies, which indicate a semi-arid to arid climate for the Bauru Group. Multiple tissues of notosuchian crocodyliforms were included in our study, as well as a testudines carapace fragment, lepisosteiform fish teeth and scales, and host rocks. The mineral textures, X-ray diffraction and stable isotope data support preservation of tooth enamel and scale ganoin bioapatite. The δ13C results point to different feeding habits between two terrestrial, carnivore notosuchians, namely a terrestrial source diet for Uberabasuchus terrificus and an aquatic source diet for Campinasuchus dinizi. The δ18Ow for the crocodyliform data was calculated and compared to other Upper Cretaceous sites. Values support dry conditions during the formation of the bioapatite for the Fazenda Três Antas site and point to the Hateg Basin in Romania, yet likely younger, as a good paleoclimatic analogue.

Sources of metals and fluids for the Taijiying gold deposit on the northern margin of the North China Craton

Recognition of the sources of metals and fluids is crucial to determine the genesis of gold deposits, especially in distinguishing the orogenic and magmatic hydrothermal deposits. There is no consensus on the source and genetic style of the Mesozoic gold deposits in the North China Craton (NCC). The Taijiying gold deposit in the Chifeng-Chaoyang gold district on the northern margin of the NCC is a medium-sized gold deposit and worth studying for its sources of metals and fluids. It is hosted by amphibole- to granulite-facies metamorphic rocks and Mesozoic intrusions, and controlled by NNE-, NE-trending compressional reverse faults and NW-trending extensional normal faults. The gold mineralization types include auriferous quartz veins and wall rock alterations of phyllic mineralization, pyritization, chloritization, and carbonatization. According to the crosscutting relationships of the veins and the mineral textures within the ore-bearing veins, four mineralization stages are recognized: clouded-white quartz ± pyrite (stage I), gray quartz + pyrite (stage II), quartz + polymetallic sulfides (stage III), and calcite ± quartz (stage IV), among which the stages II and III represent the main gold mineralization stages. The timing of the gold mineralization is constrained to the Middle Triassic by zircon U-Pb ages of a pre-metallogenic diorite (258.0 ± 1.9 Ma) and a ore-related granitic porphyry dike (241.5 ± 2.2 Ma). Three types of fluid inclusions (FIs) in the quartz veins of four stages are identified: vapor-rich (type 1), CO2-H2O three-phase (type 2), and liquid-rich FIs (type 3). Their trapping temperatures gradually decrease from 352 ℃ (stage I) to 124 ℃ (stage IV), with salinities decreasing from 9.8 to 2.0 wt% NaCl eqv., indicating that the ore-forming fluids belong to a H2O-NaCl-CO2 system. The first three stages were characterized by moderate-high temperatures, a large variation in salinities, akin to those of the magmatic hydrothermal fluids. The H-O isotope compositions from the stage II (δ18Ow = 4.1–4.8‰ and δD = -110 to −87‰) to the stage III (δ18Ow = 3.5 to 3.7‰ and δD = -101 to −98‰), indicate that the ore-forming fluids were mainly magmatic fluids. The δ34SV-CDT (1.7–2.1‰), Pb isotopes (206Pb/204Pb = 15.09–15.90, 207Pb/204Pb = 15.00–15.15, 208Pb/204Pb = 35.76–37.97), and Os isotopes (initial 187Os/188Os = 2.3 ± 1.0) of the Au-bearing pyrite samples at the stages II and III, similar to those of the crust-derived magma, suggest that the gold and other metals were extracted from the partial melting of the lower crust. Accordingly, the Taijiying gold deposit is probably a magmatic hydrothermal deposit. The areas recording the Triassic batholith with a developed fault system would be prospective targets for gold mineralization in the Chifeng-Chaoyang district on the northern margin of the NCC.

Mesoscopic and Microscopic Magmatic Structures in the Quxu Batholith of the Gangdese Belt, Southern Tibet: Implications for Multiple Hybridization Processes

The Quxu batholith of the Gangdese magmatic belt, southern Tibet, comprises predominantly Early Eocene calc-alkaline granitoids that feature a variety of types of magmatic microgranular enclaves and dikes. Previous studies have demonstrated that magma mixing played a crucial role in the formation of the Quxu batholith. However, the specific processes responsible for this mixing/hybridization have not been identified. The magmatic microgranular enclaves and dikes preserve a record of this magma mixing, and are therefore an excellent source of information about the processes involved. In this study, mesoscopic and microscopic magmatic structures have been investigated, in combination with analyses of mineral textures and chemical compositions. Texturally, most of the enclaves are microporphyritic, with large crystals such as clinopyroxene, hornblende, and plagioclase in a groundmass of hornblende, plagioclase, and biotite. Two types of enclave swarms can be distinguished: polygenic and monogenic swarms. Composite dikes are observed, and represent an intermediate stage between undisturbed mafic dike and dike-like monogenic enclave swarms. Our results reveal three distinct stages of magma mixing in the Quxu batholith, occurring at depth, during ascent and emplacement, and after emplacement, respectively. At depth, thorough and/or partial mixing occurred between mantle-derived mafic and crust-derived felsic magmas to produce hybrid magma. The mafic magma was generated from the primitive mantle, whereas the felsic end-member was produced by partial melting of the preexisting juvenile crust. Many types of enclaves and host granitoids are thus cogenetic, because all are hybrid products produced by the mixing of the two contrasting magmas in different proportions. In the second stage, segregation and differentiation of the hybrid magma led to the formation of the host granitoids as well as various types of magmatic microgranular enclaves. At this stage, mingling and/or local mixing happened during ascent and emplacement. In the final stage, mafic or hybrid magma was injected into early fractures in the crystallizing and cooling pluton to form dikes. Some dikes remained undisturbed, whereas others experienced local mingling and mixing to form composite dikes and eventually disturbed dike-like monogenic enclave swarms. In summary, our study demonstrates the coupling between magmatic texture and composition in an open-system batholith and highlights the potential of magmatic structures for understanding the magma mixing process.

The formation of (Ni-Co-Sb)-Ag-As ore shoots in hydrothermal galena-sphalerite-fluorite veins

Unusual hydrothermal native As-sulfide ± native Ag ± arsenide ± antimonide ± sulfosalt ore shoots and their co-genetic sulfide-fluorite-barite-quartz host veins, which are common in the region and in whole Central Europe, were investigated at three localities in the Schwarzwald, SW Germany, to understand the physico-chemical processes governing the change from a normal (= common) hydrothermal to an exceptional ore shoot regime. Based on fluid inclusions, the formation of the gangue minerals is the result of binary mixing between a NaCl-rich brine and a CaCl2-rich brine (both ~ 20 wt% NaCl aq.). This mixing correlation, major and minor fluid composition, formation temperature (~ 150 °C), and δ34S signature are identical (within error) in ore shoots and host veins. Thermodynamic modeling indicates that ore shoot formation must have resulted from a change in redox conditions by a local influx of a volumetrically minor reducing agent, probably hydrocarbons. The elemental content and the mineralogy of each ore shoot locality (Ag-As-rich: Münstertal; Ag–Ni-As-rich: Urberg; Ag–Ni-As-Sb-rich: Wieden) reflect the metal content of the binary mixed fluid, while mineral textures, successions, and assemblages are thermodynamically and, regarding sulfur, kinetically controlled. The formation of vein and ore shoot sulfides requires an addition of sulfide, most probably from the sulfide-bearing host rocks, because thermodynamic and kinetic reasons suggest that the two major vein-forming and metal-bearing fluids are not the source of the sulfur. The final ore shoot textures are influenced by later hydrothermal remobilization processes of As and Ag. This results in a number of sulfosalts, mostly proustite-pyrargyrite. Interestingly, the greater thermodynamic stability of Sb-endmember sulfosalts enables them to form even in As-dominated fluid systems.